The present invention relates to a method of and a device for controlling the fuel injection in an internal combustion engine. More particularly, the invention is concerned with a method of and a device for controlling the fuel injection in an internal combustion engine of the type in which an asynchronous fuel injection is conducted in response to the required degree of acceleration.
In a typical known electronic fuel injection controller, the basic fuel injection time duration, i.e. the basic time length of opening of the injector, is computed in accordance with the absolute pressure in the intake pipe and the engine speed. Then, various correcting computations are conducted on this basic fuel injection time duration in accordance with the states of operation of the engine including warming up of the engine, transient state of engine operation and so forth, thereby to determine the final fuel injection time duration. The fuel injection valve is opened for the thus determined final fuel injection time duration at predetermined crank angles or positions. This fuel injecting operation is referred to as "synchronous fuel injection".
On the other hand, when a quick acceleration of the engine is required, the fuel is injected regardless of the crank angle upon detect of the quick acceleration of the engine because, for otherwise, the driveability of the engine will be impaired if the fuel injection is not made till the predetermined crank angle is reached. This injecting operation conducted regardless of the crank angle is referred to as "asynchronous fuel injection".
Usually, the asynchronous fuel injection is conducted when the degree of acceleration has exceeded a predetermined judging or reference value. The asynchronous fuel injection in response to an asynchronous fuel injection demand is made in various forms or patterns. For instance, in one form of the asynchronous fuel injection, the fuel injection rate is maintained constant regardless of the state of engine operation. In another form, the fuel injection rate is varied in accordance with the degree of acceleration, such that the fuel is injected at a greater rate as the degree of acceleration is increased. In still another form, the fuel injection rate is varied in accordance with both of the degree of acceleration and the engine temperature, such that the fuel injection rate is increased when the degree of the engine acceleration is great and when the engine temperature is low.
In the engine operation under the asynchronous fuel injection, it is often experienced that the state of combustion is impaired by an improper air-fuel ratio of the mixture because the asynchronous injection is made, in some cases, without taking the air-fuel ratio into account. This unfavourably causes various problems such as deterioration of the engine performance, increase in the fuel consumption and worsening of the condition of the exhaust gas.
These problems are serious particularly in the lean control (feed-forward control) in which the air-fuel ratio is controlled for the leaner side under a specific condition of engine operation in order to improve the fuel consumption or in the rich control in which air-fuel ratio is controlled for richer side to obtain greater power under specific condition of engine operation, rather than in the feedback fuel injection control for maintaining the air-fuel ratio at the stoichiometric level in accordance with a signal from an O.sub.2 sensor. Namely, when the asynchronous fuel injection is conducted in the lean control or the rich control mentioned above, it is necessary to control the injection rate in accordance with the air-fuel ratio because, in such engine operation modes, the fuel is burnt under a wide variety of air-fuel ratio.